Senator says construction timeline for new I-90/SR 18 interchange still on track; new electronic warning signs coming soon

Washington State Senator Mark Mullet’s office said  Monday, September 17th that recent reports stating WSDOT is delaying construction of a new interchange at SR18 and I-90 are incorrect.

In an email to constituents Mullet disputed reports that WSDOT’s current project timetable, which anticipates construction from 2021 to 2023, broke an alleged commitment to start and finish work sooner.

“Unfortunately, stories are circulating that WSDOT promised last year that work would run from 2019 to 2022,” Mullet said. “They seem to accuse the department of trying to slip a delay past without us noticing. But that’s not true.”

The 2017 Transportation Budget accelerated access to $150 million to start the process of building the new interchange right away, instead of waiting until 2023. That budget also included funds to widen SR 18 between I-90 and Deep Creek.

According to the press release from Mullet’s office, WSDOT began work on the new interchange last year, seeking a design consultant, which it selected in December. Earlier this year it also started to conduct the necessary community engagement, environmental review and design process. In May 2018, WSDOT announced that construction would run from 2021 to 2023, a timeline that the department said still stands.

Mullet said that some initial rough estimates may have been misinterpreted and he emphasized that no official timeline was set or given until this May. In an April 2017 article, Mullet said the goal to complete the project was around 2023. Before 5th District legislators’ bipartisan effort to push up the timeline, the project wasn’t scheduled to begin until 2023.

There was a report from Snoqualmie Mayor Matt Larson in May 2017 (based on an early meeting with WSDOT) stating that construction would begin in 2019 and the project would be mostly complete in 2022, or possibly in 2023.

Senator Mullet, though, commented, “A start date of 2019 wouldn’t have given WSDOT enough time to do the necessary preliminary work to make sure the project is done right.”

WSDOT acknowledged that its process selecting a design consultant took slightly longer than anticipated, leading to a delay of about two months last year as things got started, but that delay is reflected in the 2021 to 2023 timeline.

Safety enhancements coming soon to I-90

Before construction commences WSDOT said some other safety improvements will be added to the often dangerous interchange area,  including two new electronic signs coming to I-90 this fall that will warn drivers about traffic congestion. The signs will be located two-miles and one-mile from the interchange. Next spring/summer WSDOT will extend the exit-only striping on the eastbound I-90 approach to SR 18 – that will extend just over a mile back from the exit.

Project design & milestones to date

According to the WSDOT I-90/SR 18 improvement project page they awarded CH2MHill, Inc. the contract to assist with environmental planning, developing the preliminary design, and preparing the documentation needed for the Request for Proposals from contractors interested in completing the design of an improved interchange and widening of SR 18.

A Diverging Diamond Interchange (DDI) is currently the preferred concept for a new interchange. WSDOT believes a DDI can optimize traffic flow and manage congestion better for travelers through the interchange. DDI’s are relatively new, with about 80 built nationwide. [You can see how DDI’s work in a video below.]

Planned Community Outreach

WSDOT said as it progresses through the project’s environmental planning and design phase, it will conduct “a thorough and extensive community outreach effort to people who travel the interchange or live in one of the many nearby communities.”

During the construction phase WSDOT said its key goal will be “to keep communities and neighborhoods informed about upcoming work and how construction will affect the area.” WSDOT also plans to hold open houses and community briefings during as the project progresses.

90/18 Improvement ProjectTimeline

  • 2017: Design work initiated
  • 2018: Jacobs (CH2MHill) selected to assist WSDOT in preparing the request for proposals
  • 2018-2019: Community engagement, environmental and traffic analysis
  • 2021: Construction tentatively scheduled to begin
  • 2023: New interchange opens


Tipped semi at the I-90/SR 18 interchange on Friday, April 15, 2016.

Comments are closed.


  • On the Diverging Diamond Interchange preference; please look at the last picture included in this article. The picture with the Semi truck tipped on it’s side on the shoulder of the road. With a DDI, the traffic at that location will be on the opposite side of the road. Now picture that tipped over semi truck in the DDI layout – it will be laying across the opposing lane of traffic. Hopefully without a vehicle under it.
    With the amount of truck traffic through this intersection, I don’t understand the single focus on a DDI. When you add in tourists who will be unfamiliar with the DDI, heavy rain reducing visibility, and the snow we get in winter covering the lane markings, the DDI doesn’t seem to make sense for this location. Hopefully “they” will reconsider and use a more appropriate design for this interchange.

  • Hi Danna,
    Have you received any update on plans for relocating the weigh station and potential opening up that asphalt to commuters?

    1. I don’t believe it’s been decided yet, but see if can find an update. Last I heard WSDOT and WSP wanted it near Truck Town, but the City of North Bend would rather it be near EB 90 exit 38.

  • I see this proposed solution possibly more “cost effective” than volume effective. Take a look at the Interstate 5 (I-5) State Route 18 (SR-18) interchange and imagine how efficient it handles the traffic. This would cost more at first but be a true solution not a temporary fix as the DDI represents.

  • Living Snoqualmie